Although applicable to arbitrary networks, the present invention and its underlying problem are explained with regard to a network component transmission inhibiting device of a network that is located on board a motor vehicle, namely the CAN transmission inhibit function (CANSTOP) of the real-time capable serial bus system “Controller Area Network” (CAN).
In modern motor vehicles, provision is made for network components (control units, sensor devices, actuator devices) having unique addresses and linked over a bus such as the CAN bus, the network components being able to exchange messages having a clear assignment between the same. An example of such a network component is a proximity control device which is used in a motor vehicle for automatic proximity control.
The underlying problem of the present invention lies generally in that, in certain cases, it is required to decouple such a network component from the network or to inhibit its transmission function to the network by a safety device in the form of network component transmission inhibiting device.
FIG. 2 shows such a known transmission inhibiting device for a CAN network component.
In FIG. 2, [reference numeral] 100 designates a vehicle CAN bus, 10 [designates] a controller of a proximity control device, 20 a transmission inhibit signal generating device, 15 a CAN control section of controller 10 (usually a microcontroller), 151 a TX transmission port of CAN control section 15, 152 an RX receive port of CAN control section 15, 30 a CAN transmission/receiving device, TX a transmission line, RX a receive line, CANH a CAN high-level line, CANL a CAN low-level line, S1 a switch, SS an inhibit signal line, K1 a first node, R a resistance, and V+ a supply potential.
During normal operation, controller 10, via its CAN control section 15, sends signal messages over unidirectional transmission line TX to CAN transmission/receiving device 30 from where, via CAN high-level line CANH and CAN low-level line CANL, the signal messages are sent to the remaining network components over vehicle CAN bus 100. Likewise, the controller, via unidirectional receive line RX, receives signal messages which are addressed to it from CAN transmission/receiving device 30.
With the assistance of transmission inhibit signal generating device 20, which, in the present example, is a digital signal processor (DSP) it is possible for faults to be detected in controller 10, either directly via a link (not shown) or indirectly via other components (not shown either).
In response thereto, transmission inhibit signal generating device 20 outputs an inhibit signal to switch S1 via inhibit signal line SS, the inhibit signal closing the switch and, consequently, connecting first node K1 on transmission line TX to supply potential V+. Because of this, transmission line TX is constantly at a logical “1” or “H” level, resulting in that no data, i.e., level variations H->L or L->H, can be transmitted. Consequently, the link of controller 10 to vehicle CAN bus 100 is inhibited and, therefore, unwanted or unpredictable reactions of other network components on vehicle CAN bus 100, for example, in the form of control units, can be prevented.
In this context, resistance R, which is located between first node K1 and transmission port 151 connected to transmission line TX protects TX transmission port 151 from supply potential V+.
In the above conventional design approach, it has turned out to be a disadvantage that this transmission inhibiting device, which is composed of transmission inhibit signal generating device 20, inhibit signal line SS, switch S1 and supply potential V+, cannot be tested by controller 10 without an additional testing device since the reaction in appertaining CAN control section 15, which is usually an integral component of the controller, does not furnish any clear conclusions in the OK case of the transmission inhibiting device.
In particular, the OK case (transmission inhibiting device works) cannot be distinguished from the case in which the CAN bus connection to controller 10 is interrupted, i.e., for example, in which transmission line TX and/or receive line RX and/or CAN high-level line CANH and/or CAN low-level line CANL is/are interrupted or transmission/receiving device 30 has a defect.
Since in both cases, CAN control section 15 generates the same fault flags or markers in its internal evaluable registers if, in response to an attempt to transmit a signal message over transmission line TX, it does not receive an acknowledge response via receive line RX within a certain time. In other words, in all these cases, it detects the presence of a decoupling from vehicle CAN bus 100.
Consequently, conventional methods using an additional device are disadvantageous in so far as they require a large expense and operating effort.